Net-zero emissions have been globally acknowledged as a means to mitigate climate change. The chemical industry accounts for approximately 6% of total CO
2 emissions in the United States. Lubricants are a typical chemical product, with approximately 8 million tonnes produced per year and a global market size of around $200 billion. Fossil-based lubricants dominate the market, accounting for more than 95%, and possess a high carbon intensity. Biolubricants can mitigate these problems and are primarily produced from vegetable oil and animal fats, with vegetable oil accounting for over 80% of the market share. Oils and fats can be used directly as lubricants, offering excellent viscosity indices, high flash points, and good lubricity. Oils and fats can be used directly as lubricants, offering a high viscosity index, a high flash point, and good lubricity. Additionally, these oil-based lubricants are biodegradable and environmentally friendly. However, they also exhibit some disadvantages, such as poor low-temperature performance and short oxidation stability, among others. Therefore, modifications of oils or fats, such as transesterification, hydrogenation, epoxidation, etc., were performed. Triglycerides, the basic molecules in oils and fats, are converted to fatty acid esters (FAEs) through transesterification with alcohols using acidic or basic catalysts, a process similar to biodiesel production. The resulting products have viscosities similar to those of the oil or fats, but exhibit low oxidation stability and poor low-temperature performance due to their shared fatty acid profile. Other studies have also explored transesterification using the resulting FAEs from short-chain alcohols with other polyols, such as trimethylolpropane (TMP) and neopentyl glycol (NPG). However, TMP and NPG are primarily produced from non-renewable sources, which reduces the renewability of the biolubricants. The products from transesterification FAEs with polyols significantly improve low-temperature properties. However, oxidation stability substantially depends on the source of FAEs. Hydrogenation can add hydrogen atoms to carbon-carbon double bonds in oils and fats to make them saturated. Although complete hydrogenation can improve oxidation stability, the resulting products exhibit poorer low-temperature performance. Some studies have been conducted to partially hydrogenate oils or fats by converting linoleic acid or linolenic acid into oleic acid. The resulting products have significantly improved oxidation stability while retaining their liquid state. However, partial hydrogenation occurs at high pressures and temperatures, in addition to the expensive catalysts. Epoxidation of oils or fats is converted to epoxides by reacting with peroxy acids in the presence of catalysts, such as mineral acids, acid ion exchange resins, metal catalysts, and enzymes. The resulting product exhibited improved oxidation stability, enhanced lubricity, and enhanced low-temperature performance. However, the reaction rates are limited by the mass transfer in reaction mixtures. In addition, the slow reaction rates are intentionally operated to inhibit the formation of explosive materials. Moreover, biolubricants derived from epoxidation are primarily used as greases in industrial machinery.
To overcome these limitations, ozone cracking has been applied to efficiently refine lipids, obtaining ozone intermediates at room temperature with high yields of target products. The unsaturated compounds in lipids were attached by ozone to cleveage into two typical compounds: carboxylic acids and dicarboxylic acids. Both these carboxylic acids and dicarboxylic acids can be used to synthesize the biolubricants through esterification of alcohols, diols, and ploys. The resulting biolubricants showed a broad range of viscosities from 5 to 3000 cSt, indicating suitable application for both engine mobile oil and machinery gear oil. All products exhibit a high viscosity index above 150, exhibiting reduced effects of temperature on viscosity. Experiments also show products own excellent oxidation stability by no indication of oxidation even after 100 hours of oxidation stability tests. TGA show the thermal stability ranged from 250 to 400 oC, depending on the formula of the lubricants.
In summary, ozone cracking of lipids provided a new insight into high quality biolubriant synthesis from lipids for decarbonization of lubricant industry.
